DATABASE
MANAGEMENT
SYSTEM
5. Integrity services: Mechanisms to
ensure that certain rules are
followed with regard to data in the
database and any changes that are
made in the data.
6. Data Independence: Facilities to
support the independence of
programs from the structure of the
database.
7. Replication support: A facility to
manage copies of the same data at
multiple locations.
8. Utility Services: DBMS provided
services that assist in the general
maintenance of the database.
• SHARED UPDATES
• Multiple users are making updates to the
database at the same time.
Problem:
• Multiple people updating the
database simultaneously can override
each other
Example:
• Agents T1 & T2 simultaneously read
the seats reserved on Flight 890 i.e.
80
• T1 cancels 5 seats updating the seats
reserved on Flight 890 to 75
• T2 reserves 4 additional seats on the
flight and updates the seats reserved
on Flight 890 to 84.
• If T1 updates the database before T2.
T2 will override T1’s change and make
reservations to 84 rather than getting
the correct value of 79.
• Similarly if T2 updates before T1 the
seats reserved will be 75
• SHARED UPDATES SOLUTION : Batch processing |
Locking
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